There are many applications where it is necessary to protect electrical equipment from power surges, high energy transients and high frequency noise or random voltage embedded in the power sine wave which could damage or adversely affect the operation of such equipment. Such protection is particularly important for equipment having highly sensitive or complex loads which are susceptible to power surges and high frequency content transients. For example, conventional data processing equipment includes sensitive components which are particularly susceptible to damage or loss of stored data therein due to reactive voltage spikes occurring as a result of power surges in the supply lines, switching transients, or as a consequence of external causes such as lightning which strikes the supply line or produces an electromagnetic pulse which is inductively coupled into the supply line, or reactive spiking or ringing within the load's own power supply transformers which upsets the DC output of the internal power supply. Some of these conditions may also occur with respect to, and thus damage, sophisticated telecommunication and telephone equipment installations, for example.